Means and method for crimped high frequency connectors



March-10, 1970 M. F. O'KEEFE ETAL 3,500,296

MEANS AND METHOD FOR CRIMPED HIGH FREQUENCY CONNECTORS Filed May 15, 1967 3 Sheets-Sheet 2 March 10, 1970 M. F. O'KEEFE ETA!- 3,500,296

MEANS AND METHOD FOR CRIMPED HIGH-FREQUENCY CONNECTORS Filed May 15, 1967 7 3 Sheets-Sheet 3 United States Patent 3,500,296 MEANS AND METHOD FOR CRIMPED HIGH FREQUENCY CONNECTORS Michael Francis OKeefe, Mechanicsburg, and Edgar Wilmont Forney, Jr., Harrisburg, Pa., assignors to AMP Incorporated, Harrisburg, Pa.

Filed May 15, 1967, Ser. No. 638,381 Int. Cl. H01r 17/18 US. Cl. 339-177 Claims ABSTRACT OF THE DISCLOSURE A crimping technique is disclosed as applied to the center contact member of a high frequency coaxial connector wherein a cable center conductor is terminated to such contact member through a nonintegral plug driven radially into the member against the center conductor. The plug is forced into a deforming engagement with the center conductor providing a stable mechanical and electrical connection therewith. This deformation is controlled to preclude deformation of the center contact member and prevent radial or axial extrusion of the contact member. Limiting radial or axial extrusion of the center contact member avoids displacement which could cause degradation in the radio frequency energy carried by the connector. The plug is driven flush with the outer surface of the contact member to eliminate discontinuities at the crimp site.

Embodiments are taught for plugs of circular and wedge shaped configuration and for plugs of soft and hard materials, and a method of manufacturing a preferred plug embodiment is disclosed.

BACKGROUND OF THE INVENTION With crimp type coaxial connectors made in accordance with the prior art, the center contact member is crimped by a controlled inward deformation of a portion thereof to grip the center conductor of the cable of use. In known embodiments the crimped portion is integral with the contact body and is placed toward the center of the contact. Experience has shown that there is a resulting axial extrusion of the center contact as the crimp portion is deformed inwardly. Considering that variations may be expected from part to part due to tolerances, in the cable center conductor, the center contact and in the crimping tools used to effect the crimp, this axial extrusion may be expected to vary. Experience has shown that it does and that the variation causes a small, but uncontrolled variation in the length of the contact member and in the spacing betwcn inner and outer conductive paths of the connector at one or both ends of the center contact. Even through this variation is small, it has been found to result in a signal loss which is significant and which becomes more significant as signal frequency goes up. The worst part of the matter is that standard techniques of compensation which rely upon a calculated control of conductive and dielectric parameters are of little help, since the variation is uncontrolled in terms of extent and location.

As a separate problem with crimp type center contacts having a crimp zone in the center of the contact, the inner surface of the contact member is in engagement "ice with the cable center conductor for a considerable length of the contact member. This creates a re-entrant surface which may vary depending upon axial loads on the connector and other factors tending to displace components of the connector assembly. Re-entrant surfaces cause signal loss at higher frequencies.

As still another problem with very small coaxial connectors wherein the center contact member has a wall dimension of less than ten thousandths of an inch, difiiculties have also been experienced in crimping without bending or deforming the adjacent thin wall sections of the contact member.

As still another problem, the use of a crimp portion integral with a contact member imposes a limitation on material characteristics which at times may be undesirable. For example, in many connector designs it is necessary to provide a center contact having spring portions requiring an appropriately hard and stiff material, such as hard brass or beryllium copper. The crimp portion, on the other hand, must be malleable and relatively soft. This leads either to a compromise in design or to special and expensive treatment of the contact to cause different portions of the same member to have different material characteristics.

Still another problem has to do with the type of crimp possible with an integral crimp portion. If the crimp has a smooth surface the inside will be relatively smooth, even though bulged inwardly. The lack of relatively sharp edges driven in engagement with the inner conductor has been found, at times, to provide an interface which is of a relatively high resistance, on the order of a milliohm or above. The lack of sharp inner surfaces biting into and deforming the center conductor has been found to provide a termination which may be unstable with certain types of center conductors. The use of a sharply defined crimp portion has been found to leave annular cracks on the outside of the contacts after crimping to result in a poor electrical performance and contact weakness.

SUMMARY OF THE INVENTION This invention relates to high frequency coaxial devices and more particularly to method and means for pro viding a high performance, low loss termination of coaxial cable.

It is an object of the invention to provide a coaxial connector or terminal having a crimped center contact which provides improved connector performance at signal frequencies in the kilo-megacycle range. It is another object of the invention to provide a crimpable center contact for high frequency connectors which eliminates variables introduced by deformation of center contact material. It is still another object to provide a crimpable center contact structure which minimizes the presence of re-entrant surfaces and provides a stable, low resistance connection of center contact member to cable center condoctor. It is yet another object to provide method for crimping and a structure permitting termintion of small thin wall center contact members, particularly those members having requirements of hardness or stiffness for providing spring characteristics. It is a further object to provide a method of crimping coaxial connector center contact members which leaves the outer surface thereof smooth and of constant diameter Without deforming the metal making up the center contact member. It is yet a further object of the invention to provide a method of making center contact members which may be crimped onto the center conductor of a coaxial cable for high frequency use.

In the drawings:

FIGURE 1 is a longitudinal and sectional view of a coaxial connector positioned to join the ends of coaxial cable with the center contact members thereof crimped to the cable center conductor in accordance with the prior art;

FIGURE 2 is a longitudinal view of a center contact pin member in accordance with the invention having the center conductor of the coaxial cable positioned therein and prior to crimping;

FIGURES 3 and 4, are cross-sectional views of the structure of FIGURE 2 taken along lines 3-3 and 4-4;

FIGURE 5 is a longitudinal view in partial section showing the contact structure of FIGURE 2 following crimping;

FIGURE 6 is a cross-sectional view taken along lines 6-6 of FIGURE 5;

FIGURES 710 are perspective views showing a method of manufacturing a contact pin like that shown in FIG- URE 2;

FIGURE 11 is a longitudinal view in partial section of a center contact pin in an alternative embodiment, prior to crimping;

FIGURE 12 is a cross-sectional view taken along lines 12-12 of FIGURE 11;

FIGURE 13 is a longitudinal view in partial section of the structure of FIGURE 11, following crimping;

FIGURE 14 is a cross-sectional view taken along lines 1414 of FIGURE 13;

FIGURE 15 is a longitudinal view of a center contact pin member in accordance with yet another embodiment of the invention, prior to crimping;

FIGURE 16 is a cross-sectional view taken along 16-16 of FIGURE 15;

FIGURE 17 is a longitudinal view of the structure of FIGURE 15 following crimping; and

FIGURE 18 is a cross-sectional view taken along lines 1818 of FIGURE 17.

The foregoing problems are overcome and the foregoing objectives are attained through the present invention by a method and means which features a center contact member having a non-integral plug or plugs driven inwardly of the member to deform the center conductor of a coaxial cable and terminate such to the contact member. The' plug structure is driven inwardly to a point so that the outside or end portion is left flush with the outside surface of the center contact member to prevent discontinuities. The use of a plug structure which is not integral with the material of the contact member precludes axial displacement of the contact member to eliminate discontinuities caused thereby and to prevent component and tooling tolerances from becoming a factor in the performance of the connector as a high frequency transmission path. In one embodiment the plug structure is made to be relatively soft so as to undergo substantial deformation inwardly of the contact member providing a positive engagement of freshly worked conductive surface to in turn provide a stable interface of low resistance between the cable center conductor and the contact member. In another embodiment the plug structure is made to be relatively hard so as to cause substantial deformation of the cable center conductor. In both embodiments the plug structure is located close to the entry end of the contact member to reduce the presence of reentrant surfaces causing loss at high frequencies. In both embodiments the plug structure and the resulting crimp permits the use of center contact member material which is relatively independent of crimp requirements and may be quite hard and stiff to provide spring characteristics. A method for manufacturing one embodiment of the center con act number of the nv ntion is taught which yields a low cost crimp type contact member having a greater reliability than heretofore available.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to FIGURE 1, there is shown a typical coaxial connector construction interconnecting coaxial cables 10 to provide a coaxial transmission path therebetween. The cables 10 each include a center conductor 12, typically of stranded copper wire, surrounded by a dielectric sheath 14 and a braided outer conductor 16 which is overcovered by an insulating and protective sheath 18. The connector shown as 20 includes a plug half 22 and a jack half 24, each comprised of an outer metallic shell, a dielectric insert and a center contact member of conductive material crimped to the cable center conductor 12. The connector halves 22 and 24 are held together by a nut 26 rotatably mounted on 24 and internally threaded at its forward end for mating with 22. Each of the connector halves 22 and 24 includes a rear sleeve extension, shown as 28 relative to half 22, which has an inner diameter approximating the entire inner diameter of the outer conductor 16 and through which is fitted the dielectric sheath of the cable carrying the cable center conductor. The sleeve extension 28 is made sufficiently rigid to withstand crimping forces applied thereto by a. ferrule shown as 30 crimped down over the cable outer conductor 16 and inwardly against 28. This crimp serves to terminate the cable outer conductor to the outer conductive path formed by the outer shell of each half of the connector. The ferrule 30 is made to extend back over the sheath 18 and is crimped inwardly to lightly grip the sheath and provide mechanical support to the cable. Each connector half includes a dielectric insert relieved at the rear end as at 32 to receive the dressed end of the sheath 14 and a central bore shown as 34 carrying a contact member. The contact member for the connector half 22 is shown as 36 and comprises a contact pin. The member 36 is crimped to the cable center conductor by the crimp shown as 38 which is in accordance with prior art techniques heretofore mentioned.

The forward end of the insert 32 is relieved as at 40 to intermate with the insert of half 24. This insert is shown as 42 and carries a contact member 44 which includes spring finger members at the forward end thereof adapted to mate with the forward portion of contact member 36. The contact member 44 is crimped as indicated inFIGURE 1 to the center conductor of the cable.

The enlargement of the inner bore of 22 and 24 in the portions thereof overlying the center contact members is controlled relative to the dielectric material of the insert to adjust the characteristic impedance of the connector to compensate for the enlarged diameter represented by the contact members relative to the center conductors of the cable. It has been found that two of the more critical areas in a connector of a construction like that shown in FIGURE 1 are those areas wherein the electric field of the signals transmitted through the connector undergoes maximum distortion. These areas are at the points of change in diameter including the point where the outer conductor has an increased bore and the point where the center conductor enters the center contact member. The dimensions shown as A and B in FIGURE 1 cover the zones of maximum field distortion between these two points for each connector half. One of the problems with prior art devices like that shown in FIGURE 1 is that tolerances cause a variation in the axial displacement of the contact members due to an axial expansion when the center contact members are crimped. This variation causes a variation in the dimensions A and B and a variation in the pattern of the electric field in the portions of A and B. Axial displacement of the center contact members also causes a variation in the spacing between the inner ends of the contact members represented by dimension C, as well as variations in the dimensions E and F. Attempts to adjust characteristic impedance in these areas to provide a constant characteristic impedance or to provide a characteristic impedance which is controlled for the purpose of providing compensation can result only in a fixed dielectric and conductive structure which is good only for fixed conditions. This, of course, cannot be expected to work where the variations previously mentioned occur.

It will be observed from FIGURE 1 that the crimp of the contact members to the cable center conductor occurs toward the center of the contact members leaving a substantial portion of the center conductor within the bore of the contact members in engagement with the conductive material but not terminated thereto. At high frequencies the very slight space and path within the center contact member defines a re-entrant surface which can cause signal degradation. It will also be observed that at least the contact member 44 contains spring finger members which require a stiffness and hardness of the contact material to provide spring characteristics. On the other hand, both contact members must be of a relatively soft and malleable material in the zone of crimp to permit working without fracture and to minimize the forces required of tooling and to minimize die wear.

With the structure of the coaxial connector shown in FIGURE 1 in mind, reference is now made to FIGURE 2 which shows a center contact member in a pin configuration made in accordance with the invention. This member is shown as 50 and would be used in the position of 36 in the connector shown in FIGURE 1. It is to be understood that a member similar to 50, but having spring fingers on the end thereof, would be used in lieu of the contact member 44 in the connector of FIGURE 1. The member 50 includes a body of conductive material shown as 52, with a contact pin 54 at one end and a bore 56 at the opposite end. This bore is of a diameter to receive the center conductor of the cable shown as 12' in FIGURE 2. In accordance with the invention the outer wall of member 50, at one end overlying the bore, includes a plurality of apertures shown as 58 and 60. Fitted within each of the apertures is a plug, shown as 62 and 64. The configuration and position of plugs 62 and 64 can be discerned from FIGURES 2, 3 and 4. It is to be noted that the plugs are positioned with the inner ends thereof approximately flush with the wall of 56. Both plugs are arranged to be held within the apertures in the position shown in FIGURES 2-4, against accidental dis placement. This holding may be accomplished as hereinafter described relative to a preferred method of producing the member 50 or by any other suitable means, including the use of some adhesive or a flash plating. It is contemplated that the plugs may be held by making them slightly oversized relative to the apertures to provide an interference fit, but if this is done care must be taken so that in driving the plugs inwardly the surrounding material of the member 50 is not bulged or otherwise deformed from its circular configuration.

FIGURES 5 and 6 show the plugs driven inwardly to terminate the inner conductor 12 to the member 50 by a pair of dies 68' and 70 which may be formed from standard needle nose pliers or, if desired, carried in a standard straight action tool. As can be discerned from FIGURES 5 and 6, this results in a considerable deformation of the plug members and of the conductive strands of the inner conductor 12. The length of each plug member relative to its material hardness and relative to the hardness of the conductive strands must be controlled so as to avoid severing of the conductive strands, but at the same time permitting a substantial working of the materials to break through oxides formed thereon and to extrude conductive material having a fresh surface into engagement to provide a stable and low resistance interconnection of the inner conductor and the contact member. Also, the plugs must not be so soft as to deform appreciably before being driven inwardly. These factors are all, of course, related to the requirement that the plugs be driv- 6 en in a displacement controlled to leave the plug ends flush with the surface of 50.

With the plugs driven into the position shown in FIGURES 5 and 6, the outside surface of the contact member will be left substantially smooth and the contact member will not have been displaced by an extrusion, as in the case of the prior art devices utilizing an integral humped portion in the crimp zone. It is to be noted that the plug members are located quite near the entry end of the contact member so as to minimize re-entrant surfaces. With the structure shown in FIGURES 2-6 the material of 50 may be quite hard and stiff, the material of the plugs being soft and malleable. For example,

. the member 50 may be hard brass, beryllium copper,

stainless steel or the like with the plugs being of soft brass or hard copper.

In an actual embodiment and with a contact member 50 made of hard brass of a diameter approximately 0.120 of an inch, bored to 0.100 of an inch, the plugs 62 and 64 were made of one-half hard brass in a cylindrical configuration approximately 0.062 of an inch in diameter and approximately 0.038 of an inch long. The plugs were driven inwardly in the manner shown in FIGURES 5 and 6 against a seven strand, EDP tinned-copper conductor. This connection was found to provide a stable and low resistance connection of conductor to contact member, on the order of 15 to 20 micro-ohms, which evidenced excellent tensile pull-out characteristics and which provided a low-loss high frequency connection when utilized in a high frequency coaxial connector.

FIGURES 7-10 show various steps in a preferred method of manufacturing the contact member 50 heretofore described. In FIGURE 7 the contact member 50 is shown as a piece of solid stock having the end portion thereof 54 machined to a pin configuration. It is to be understood that a contact member carrying a spring configuration would be made in the same way. It is also contemplated that the steps hereinafter to follow could be performed prior to machining the forward end of the member. FIGURE 8 shows the member 50 having a single hole drilled therethrough to form what will become the apertures 58 and 60. FIGURE 9 shows the next step including the insertion of a cylindrical rod which will form plugs 62 and 64. FIGURE 10 shows the next step which includes providing an axially drilled hole forming the bore 56 of a contact member. In drilling the bore 56 a working of the material of the rod and of the member 50 will further secure the plugs to the contact member by dragging a slight amount of material of the rod along the bore. After the step in FIGURE 10 the assembly of parts may then be overplated with copper to further secure the plugs in the contact member against accidental displacement until the time of use. A suitable noncorrosive plating of silver or gold with or without an underplating of nickel, may be then employed if desired. Care should be exercised in very small parts wherein the wall thickness of the contact member is quite thin against securing the plug members to an extent causing deformation of the contact member during displacement of the plug members in use. From the foregoing it should be apparent that while the plug members are secured against accidental displacement they should be readily movable and slidable under the force of dies driving the plugs inwardly.

It is contemplated that a single plug may be utilized which would drive the strands of the inner conductor inwardly and deform such against the opposite surface of the bore of the contact member. It is also contemplated that more than two plugs may be utilized. A structure carrying four plugs would be made by the same method indicated in FIGURES 7-10.

FIGURES 11-18 relate to an alternative embodiment of a contact member shown as 72 and the same general configuration as 50, heretofore discussed. In the embodiment of FIGURES 11-18 a single plug of a wedge configuration is shown as 74. The wedge 74 has a dimension at the top which matches with an ablong aperture shown as 76 in the wall of member 72. FIGURES 13 and 14 show the wedge 74 driven inwardly to terminate a center conductor to the contact member. With the wedge in the position shown in FIGURES 13 and 14 the outside surface of the contact member is left smooth and free of discontinuities. The wedge is positioned toward the end of the contact member to reduce re-entrant surfaces.

FIGURES 15 and 16 show a contact member 78 having a plug 80 with a rectangular cross-sectional configuration. The plug 80 has a leading edge beveled as at 82 to facilitate movement of the plug relative to the strands of the center conductor without tending to cut the center conductor. FIGURES 17 and 18 show the plug 80 driven inwardly to terminate the conductor to the contact member.

In the embodiment described relative to FIGURES 2-10 the plug was taught as being relatively soft and malleable. It is contemplated that with respect to the plug shown in FIGURES 11-18 the plug material would be relatively hard and deformation resistant. The crosssectional views of FIGURES 14 and 18 show that when the plugs are driven inwardly the conductive strands of the inner conductor are deformed to a greater extent than is the case with the soft plugs. With these latter embodiments the volume of the wedge 74 and the plug 80 is controlled relative to the volume of the bore of the contact members in the zone of crimp so as to cause the conductive material of the center conductors to substantially fill the inside of the bore after deformation in the manner shown in FIGURES 14 and 18. The working of the strands of the center conductor under drive of the wedge and plugs provides an interconnection between the strands and the surface of the bOre of the contact members and provides mechanical pulling against axial pull-out of substantial strength. With regard to the latter embodiments, care should again be taken so that after the wedge or plug have been driven inwardly the outside surface of the contact members is left undisturbed and undeformed. With the concept of relatively hard plugs an even further variation in material characteristics is possible and the utility of the invention is extended to accommodate cables having center conductors of material other than stranded EDP copper.

In use the latter embodiments evident in FIGURES 11-18 may be carried by an interference fit prior to use or may be carried in loose piece form separately to be supplied one for each contact member during installation of the contact member onto a cable. It is contemplated that the use of relatively hard or soft material can be applied to either the rod or wedge plugs and that other structures including a rolled or hollow formed pin may be used for the plug or wedge members.

It is also fully contemplated that the invention may find use with solid conductors of various materials.

Having now disclosed the invention in terms intended to enable a preferred mode of practice thereof the invention is defined through the appended claims.

We claim:

1. In a device for use in carrying signals in the kilomegacycle frequency range to terminate or connect coaxial cable of the type having a center conductor surrounded by a dielectric medium and an outer conductor, a conductive body having a bore including portions of substantially constant diameter, means on the rear of said body adapted to terminate the outer conductor of coaxial cable thereto, a dielectric insert fitted within said bore adapted to receive and position a center contact member coaxial to said bore, the said center contact member including a forward mating portion and a rearward portion of substantially constant outer diameter positioned in the region of the bore of such body having a constant diameter, said contact member including an inner bore to receive the center conductor of coaxial cable, an aperture in said contact member leading to the said bore, a plug member fitted within said aperture and driven inwardly of said contact member to a point with the outside end thereof flush with the outside surface of said contact member and with the inside end thereof deforming the cable center conductor to effectively terminate said center conductor to said contact pin member without deforming said contact pin member whereby to provide a termination of the cable inner conductor with proper signal reflection being maintained in the said portions of constant diameter of said body and said center contact member.

2. The device of claim 1 wherein the said plug member is comprised of a malleable material and is of a length to be substantially deformed upon being driven inwardly to terminate the center conductor to said contact member.

3. The device of claim 1 wherein said plug member is of a material which is relatively hard as compared with the material of the cable center conductor or of the material of said contact member whereby to be relatively undeformed upon being driven inwardly to terminate the center conductor of the cable to said contact member.

4. The device of claim 1 wherein the said aperture is located at a point proximate the entry end of said contact member.

5. In a device for use with signals in the kilomegacycle frequency range in connecting or terminating coaxial cable of the type having a center conductor surrounded by a dielectric medium and an outer conductor, a conductive body having a bore of substantially constant diameter portions, means on the rear end of said body for terminating said body to the outer conductor of a coaxial cable, a dielectric insert fitted within said bore and a center contact member fitted within said dielectric insert and held coaxial relative to said bore and against axial movement relative thereto, the center contact member being comprised of a conductive material of a given hardness and including a relatively thin walled portion defining a bore to receive the inner conductor of coaxial cable, at least one aperture disposed in the thin walled portion proximate the entry end of said bore, a plug member driven into said aperture into deforming engagement with the center conductor of a coaxial cable inserted therewithin to mechanically and electrically terminate said center conductor to said contact member, the said plug member having a length and material characteristic so as to be driven substantially flush with the outside surface of said contact member without deforming said contact member whereby to preclude the presence of a discontinuity at the site of termination of said center conductor to said contact member.

6. The device of claim 5 wherein said plug member is of a material having a hardness less than that of said given hardness.

7. The device of claim 5 wherein said plug member is of a material having a hardness greater than said given hardness.

8. As an article of manufacture a contact member for use in coaxial devices of the type employed with signals of the kilomegacycle frequency range comprising a body of conductive material of a given material hardness including on one end thereof a contact portion for mating engagement with a further contact member and at the other end a bore extending within said body to receive the center conductor of a coaxial cable, said body having a smooth circular outer surface overlying said bore, at least one aperture in said body near said other end extending into said bore, a plug member positioned within said aperture with one end extending inwardly to the surface of said bore and the other end projecting outwardly of said body, means shearably securing said plug member to said body in said position against accidental displacement, said means being comprised of conductive material extended between the surfaces of the plug member and the contact member body, said plug member having a length permitting a forced displacement inwardly of said bore with the outer end of said plug being substantially flush with the outer surface of said contact member and the inner end driven into a deforming engagement with a cable center conductor in said bore to provide a termination thereof and maintain the smooth circular outer surface of said body.

9. The article of claim 8 wherein said conductive material is formed of plating material deposited on the outer surface of said contact member and said plug member.

10. In a method of manufacturing a contact member for use with high frequency coaxial connectors the steps comprising machining a rod of conductive material into a cylindrical form, drilling a hole through said cylindrical form substantially transverse to the length axis thereof positioning a malleable member in said hole extending through said form and out from the outside surfaces thereof on each side of said hole and drilling a bore References Cited UNITED STATES PATENTS 1,346,506 7/1920 Mollerhoj 287-79 2,259,261 10/1941 Miller et a1. 17484 2,999,703 9/1961 Myers 287-78 X 3,264,602 8/1966 Schwartz 339--177 3,354,420 11/1967 Mineck 339177 RICHARD E. MOORE, Primary Examiner US. Cl. X.R. 

